Return to the Ora Formation

July 9th, 2013

8_MudVolcano070913MITZPE RAMON, ISRAEL–The last location Wooster Geologists in Israel visited today was on the southern edge of the Makhtesh Ramon structure (N 30.58209°, E 34.89375°). Here are excellent exposures of the Ora Formation (Upper Cretaceous, Turonian). This curious feature was a challenge to the students to interpret. I also got it wrong in my explanation on the outcrop, so listen up Steph, Lizzie and Oscar! The students are standing in a portion of the outcrop that is mud with suspended blocks of limestone. This is a cross-section of a diapir, or body of sediment that has moved upwards through the rocks that cap it. This was caused by water-saturated sediment being compressed by the sediments above, forcing it upwards through cracks and crevices. What I got wrong was that the flat strata on top of the mud was present when the diapir formed. (I said it came later.) The mud never reached the surface to become a mud volcano. This is why the resistant beds below are bent downwards — the upward force of the mud flow was stopped by the capping rock, thus deflecting the edges of the units below. A complicated story — which is one of the many things that makes the Ora Formation interesting.

9_Oysters070913Also in the Ora Formation at this same site is a half-meter-thick unit composed entirely of oyster shells. Many of the oysters are encrusted with other oysters and, who knows, maybe bryozoans as well. (And no, Paul Taylor, I didn’t see any here yet!)

10_Hardground070913The Ora Formation also has a fabulous carbonate hardground, which was a cemented seafloor surface. We can tell this particular surface was hard rock on the Cretaceous seafloor because of all those little holes. These are the borings of bivalves known as Gastrochaenolites. They could only be made by grinding away at a cemented substrate.

Hardgrounds, oysters, odd diapirs … opportunities for future study! Israeli geologists have done fantastic work with this unit, so there are many collaborations possible here.

The Ora Formation: A future student project?

May 27th, 2011

MITZPE RAMON, ISRAEL–I’ve always enjoyed seeing the Ora Formation, which is exposed only in Makhtesh Ramon and to the south. It is early Late Turonian in age, so it is part of the Upper Cretaceous and about 90 million years old. It has an astonishing range of depositional units, many of which Will and I saw today on our way to our localities. The Ora Formation has been very well studied by Israeli paleontologists and stratigraphers. Their work can now be expanded with more paleoecological analysis and some of the insights we’ve gained from new ideas about Calcite and Aragonite Sea alternations. Maybe another Wooster Independent Study project or two in the future?

A carbonate hardground in the Ora Formation. The holes were drilled by lithophagid bivalves, producing a trace fossil called Gastrochaenolites. These borings are very densely packed, which is more typical for the Jurassic than the Cretaceous.

A unit composed of almost entirely oyster valves in the Ora Formation. It is above what is called locally the “Vroman Bank”. The shells are like large cornflakes. We didn’t get a chance to look in detail, but I’d love to see what kind of sclerobionts are preserved on these oysters.

Will is sitting in an unusual diapiric structure in the Ora Formation. This is a dissected “mud volcano“, or at least what would have been a mud volcano but for the resistant capping rock. Soupy mud was forced out from underneath the overlying limestones forming an inverted cone in cross-section. The limestones dip into the structure because they were forced down by the accumulating mud. The criss-cross lines in the mud are planes of gypsum that intruded the sediments later. Note the blocks of limestone in the “throat” of the structure — this means the limestones were lithified during the event.

Stony bryozoans get their day

August 1st, 2010

Trepostome ("stony") bryozoan on a carbonate hardground from the Kanosh Formation (Ordovician, Whiterockian) of west-central Utah.

KIEL, GERMANY–The first day of the International Bryozoology Association meeting is traditionally devoted to workshops where participants can listen to experts on a particular group, technique or idea and then ask questions, work out exercises, or study specimens. I went to the workshop on a group of extinct bryozoans called trepostomes. The Order Trepostomata usually produced thick skeletons of the mineral calcite so they are commonly known as “stony bryozoans”. They lived from the Ordovician into the Triassic, and then disappeared forever. They are a difficult group to work with because their diagnostic features are internal and microscopic (thus requiring thin-sections or acetate peels to identify) and the number of important defining characters is still debated. I went to this workshop because Ohio can be considered the Trepostome Capital of the World with its abundant and diverse varieties found in the Ordovician of the Cincinnati area. Any Wooster geology student who has taken the Invertebrate Paleontology course will remember the buckets of these fossils we’ve collected over the years on field trips.

Wooster played a small role in this workshop, to my delight. One of the interesting and somewhat odd trepostome bryozoan types is found in the Ordovician (Whiterockian) at a place called Fossil Mountain in the western desert of Utah. A generation of Wooster Independent Study students worked here with me studying carbonate hardgrounds and the fossils associated with them. We collected many examples of a strange bryozoan we called “Trepostome Species A” because we could not identify it. Later Andrej Ernst, Paul Taylor and I described it as a new genus: Kanoshopora. It is still odd with its variable walls and colony forms. This meeting may have stirred some interest in pursuing its functional morphology (essentially how it lived) and evolutionary placement. A nice contribution from those days in the late 20th Century when we walked up and down the sunny slopes of Fossil Mountain trying to sort it all out.

Longitudinal thin-section view of Kanoshopora droserae showing its complex zooecial walls.

Fossil Mountain, west-central Utah -- the scene of much Wooster geology Independent Study fieldwork in the 1980s and 1990s, and the home of many of the oldest and strangest trepostome bryozoans.

Another beautiful fossil hard substrate

May 21st, 2010

Megan Innis studying the Ripley Formation rockground near Greenville, Alabama.

GREENVILLE, ALABAMA — I have a soft spot for hard places.  (Always wanted to say that!)  Much of my career has been spent studying marine hard substrates and the communities that have evolved on and in them.  These include rocks, hardgrounds and shells on seafloors which have been encrusted and bored by diverse organisms for hundreds of millions of years.  In all the many marine environments where these substrates occur, we know the organisms faced one common problem: how to occupy and defend space in an essentially two-dimensional world.  This provides a thread to follow through the long evolution of sclerobionts (hard-substrate dwellers, to use one of my favorite words.)

At the top of the Maastrichtian (Upper Cretaceous) Ripley Formation is a rockground which was bored and encrusted on the seafloor in the classic way.  It was ably described in a paper by Jon Bryan, and we were pleased to see that the surface is still exposed and accessible today.  There were some tasty encrusting bryozoans on some of the cobbles here!

Spondylid bivalve encrusting the Ripley Formation rockground.

The joy of thin-sections

December 30th, 2009

A beautiful view of a modern hardground in thin-section.  The platy orange, pinkish and brown grains are the mineral biotite (a mica), the gray and white angular grains are quartz, and the tan irregular grains are recrystallized shells and cements.  Sampled dredged from about 650 meters in the Strait of Messina between the Italian mainland and Sicily.  Collected by Agostina Vertino.

A beautiful view of a modern hardground in thin-section with cross-polarized light. The platy pinkish and brown grains are the minerals muscovite and biotite (micas), the gray and white angular grains are quartz, and the tan irregular grains are recrystallized shells and cements. Sample dredged from about 650 meters in the Strait of Messina between the Italian mainland and Sicily. Collected by Agostina Vertino.

WOOSTER, OHIO–Bitterly cold Ohio days are perfect for geological lab work, especially with thin-sections under a warm microscope accompanied by a music-filled iPod. The next best thing to fieldwork. A thin-section is a slice of polished rock glued to a microscope slide and then ground down to a standard thickness of 30 microns so that light easily passes through it. Minerals, fossils and other internal features become visible in a thin-section which would otherwise go unnoticed in the hand sample. We use polarized light to reveal optical properties of the crystals for identification and analysis. Often a thin-section in cross-polarized light shows an astonishing array of colors, fabrics and textures.

What is most fun is to take a drab rock and find the microscopic treasures within through thin-sectioning. For example, this is the rock I worked with today:

A hardground sample from the Strait of Messina (the same rock as seen in the thin-section above).  This sample was dredged from the deep-sea and is encrusted by the coral Desmophyllum dianthus and tiny tubeworms.  Collected by Agostina Vertino.

A hardground (cemented seafloor) sample from the Strait of Messina (the same rock as seen in the thin-section above). This sample was dredged from the deep-sea and is encrusted by the coral Desmophyllum dianthus and tiny tubeworms. Collected by Agostina Vertino.

A sample of the same hardground as above with the organic material removed.  On the right is a closer view of the sand-sized grains making up the rock.  Notice that even in this view you can tell that the grains are poorly cemented to each other -- the rock is very crumbly.

A sample of the same hardground as above with the organic material removed. On the right is a closer view of the sand-sized grains making up the rock. Notice that even in this view you can tell that the grains are poorly cemented to each other.

An Italian colleague (Agostina Vertino of the Dipartimento Scienze Geologiche – Università Catania) and I are examining these unusual hardgrounds from deep in the underwater canyon at the bottom of the Strait of Messina. This is a very energetic system (the currents are fast), so the grain size is surprisingly coarse for a deep-water deposit. The composition of the sediment is highly variable, ranging from feldspars and micas to shell fragments and microscopic skeletons of foraminiferans. Our first question is the simplest: How are these sediments cemented? The thin-sections show us.

Carbonate rock fragments in the Strait of Messina hardground showing a thin fringe of calcareous cement (probably aragonite) precipitated on their edges.  The cement is formed when these crystalline fringes intersect and hold the grains together.

Carbonate rock fragments in the Strait of Messina hardground showing a thin fringe of calcareous crystals (probably aragonite) precipitated on their edges. The cement is formed when these crystalline fringes intersect and hold the grains together.

As you would expect, a rock so lightly cemented crumbles easily, and it has a very high porosity and permeability. It is remarkable that such an unstable substrate serves so well as an attachment surface for encrusting organisms such as corals, tubeworms, bryozoans and sponges.

The dark areas in this thin-section view (as in the others) are open spaces.  This particular hardground is highly porous and permeable.

The black areas in this thin-section view (as in the others) are open spaces. This particular hardground is highly porous and permeable. Note the bright fringing cements on the grains.

The porosity and permeability of this sediment is undoubtedly a key to its cementation. Fluids could move quickly and in considerable volume through this deposit, gradually precipitating the tiny, tiny calcareous crystals on the exposed grain surfaces. It is also possible that dissolving aragonite shells in the sediment supplied the necessary carbonate for the cement. There is much work ahead to figure that one out.

We will post more portraits of our geological laboratory studies this winter as we simultaneously prepare for next summer’s fieldwork. This is the life!

Wooster Geologist in Ohio!

December 16th, 2009

CAESAR CREEK STATE PARK, OHIO–I’ve definitely extended my field season as far as possible.  (And what a season it has been.)  My last fieldwork at the end of this research leave was in Ohio, about three hours south of Wooster.  I visited Caesar Creek State Park this morning where a large cut through an Upper Ordovician section has been set aside as a fossil preserve of sorts.  It is an emergency spillway for Caesar Creek Lake, which is maintained by the US Army Corps of Engineers.  Many Wooster paleontology field trips have stopped here.  Fossils can be collected, but only with a permit (obtained at the visitor center) and following significant regulations.  The fossils are diverse and abundant, including all the stars of the Ordovician seafloor.

My task was to find, photograph and measure an old trace fossil friend: the boring Petroxestes pera.  This is a slot-shaped excavation in carbonate hard substrates formed by bivalves (probably in this case the modiomorphid Corallidomus).

The boring Petroxestes pera (the name means "purse-shaped rock-grinding") in a hardground at Caesar Creek State Park.

The boring Petroxestes pera (the name means "purse-shaped rock-grinding") in a hardground at Caesar Creek State Park.

These elongated holes are among the first bivalve borings.  Some of my students and I think they may have been formed in clusters, and they also may be oriented relative to each other and their local environment.  In any case, I found plenty.  It was an astonishingly cold morning, though, so I didn’t waste any time on the outcrop!

Yes, this photo is here mainly to show just how tough Wooster Geologists are.  And there are some very nice brachiopods and bryozoans!

Yes, this photo is here mainly to show just how tough Wooster Geologists are. And there are some very nice brachiopods and bryozoans!

Middle Cambrian stromatolites high in the Canadian Rockies

August 9th, 2009

FIELD, BRITISH COLUMBIA, CANADA–Our study group was fortunate to meet Whitey Hagadorn (Amherst College and Denver Museum of Natural History) and Sally Walker (University of Georgia) for a hike to an exposure of stromatolites in the Pika Formation (Middle Cambrian) near Lake Helen and Lake Katherine in Banff National Park. A stromatolite is a finely-laminated sedimentary rock produced by mats of cyanobacteria in a shallow sea collecting and trapping thin layers of sediment. They are relatively common features in Precambrian sediments (the oldest of fossils, in fact) and become significantly more rare in younger rocks (although they are still around today). These Cambrian stromatolites are interesting because of what they can tell us about Cambrian marine conditions, including tidal dynamics, bioturbation, and grazing herbivore pressures.

stromatoliteoutcrop080809

Stromatolites exposed as domal structures in this eroding outcrop of the Pika Formation (Middle Cambrian) above Helen Lake in Banff National Park.

A natural cross-section of the Pika Formation stromatolites showing their laminated nature and sediment which has accumulated around their heads.

A natural cross-section of the Pika Formation stromatolites showing their laminated nature and sediment which has accumulated around their heads.

A hardground (light unit) exposed in cross-section in the sediment between stromatolite heads.  This is a layer of carbonate sediment which was cemented on the seafloor and then eroded by currents.  The dark sediment was deposited later on top of the scoured surface.  The hardground layer had been previously burrowed when still soft.

A hardground (light unit) exposed in cross-section in the sediment between stromatolite heads. This is a layer of carbonate sediment which was cemented on the seafloor and then eroded by currents. The dark sediment was deposited later on top of the scoured surface. The hardground layer had been previously burrowed when still soft.

Beautiful folds in the rocks above the Pika Formation stromatolites.  They are nearly recumbent in some parts.  I'll leave their interpretation to my structural geologist colleagues Sam Root and Shelley Judge!

Beautiful folds in the rocks above the Pika Formation stromatolites. They are nearly recumbent in some parts. I'll leave their interpretation to my structural geology colleagues Sam Root and Shelley Judge!

A marmot on the banks of Helen Lake.  Not at all camera shy, this little guy.

A marmot on the banks of Helen Lake. Not at all camera shy, this little guy.

Thoughts on Future Wooster Geology Research in Russia

June 17th, 2009

I was very impressed by the Ordovician rocks I saw in the Leningrad Region on this past trip.  I had seen parts of the Ordovician System in Estonia nearby, but not to this extent nor this particular facies.  My model for Ordovician rocks had been based too strictly on those I’ve worked with in North America.  Now I realize that the environmental conditions and faunas were significantly different on the ancient continent of Baltica — enough to produce unexpected trace fossils, especially on and in the hardgrounds.  My perspective was changed, and thus the kinds of questions my students and I will be addressing in the next few years.

Nikolai, Sergei, Andrei, me, and my host Andrey in the Sablino Mines. I really don't know why there was a decorated Christmas tree in this cavern!

Nikolai, Sergei, Andrei, me, and my host Andrey in the Sablino Mines. I really don't know why there was a decorated Christmas tree in this cavern.

My Russian host, Andrey Dronov, was extremely generous and patient, freely sharing with me his scientific thoughts and his passion for Russian history and culture.  I could not have asked for better.  Remarkably, I met him for the first time on this expedition.  My other Russian colleagues were great fun, and they also taught me much about Russia and its geology.

I learned that field geology in Russia is difficult and certainly could not be done without a knowledgeable Russian host.  Every outcrop was farther, muddier, steeper and more overgrown than I expected.  In fact, we looked at outcrops American geologists would have given up on years ago.  If the rocks were there, we found them by hacking through the vegetation and digging them out with shovels.

Do you see the outcrops of limestone along the banks of the Lynna River?  Neither do I.  They are there, though, and Andrey and I found them with an epic jungle journey.

Do you see the outcrops of limestone along these banks of the Lynna River? Neither do I. They are there, though, and Andrey and I found them with an epic jungle journey on our last field day.

The major catch to doing Independent Study work in Russia for a student is that we could not take specimens back to Wooster.  We could, though, work in the geological lab facilities at the Academy of Sciences in Moscow, collecting enough data and images to keep a student busy for a year back home.  I would look forward to showing a student these unusual rocks and fossils, and I now know how better to prepare for work in Russia!

Goal!

June 8th, 2009

BABINO, LENINGRAD REGION, RUSSIA–Today we visited an active quarry, which is a different experience from the riverbank exposures and abandoned quarries we have been frequenting.  Quarry mud has a special character — a kind of purified mud, the kind of mud all mud aspires to be.  There are also very large trucks splashing by, giant rock saws whining, cranes lifting large blocks, and small groups of curious workmen who want to see what we are doing there with our hammers that now seem so small.  Active quarries can produce the very best exposures for geologists, especially those interested in the boundaries between rock units as we are.  This quarry at Babino N60.03035°, E32.38613°) is particularly good because they quarry Ordovician limestone by first cutting it vertically, and then lifting the rocks away in sections, revealing smooth surfaces perpendicular to bedding.

Cut surface through Ordovician section, Babino Quarry.

Cut surface through Ordovician section, Babino Quarry.

I want most to see the boundary between the Lower and Middle Ordovician rocks, and look at the trace fossils above and below it.  This boundary — a plane in the rocks which extends across northeastern Russia, Scandinavia, and parts of northern Europe — could not be better displayed than the way we saw it here.  It is an erosional surface which has been cemented into a carbonate hardground and then bored (to some extent that we are debating) and abraded smooth.  Above it is a significant change in the fossil fauna, a change which can be seen around the world.  In no place is this boundary better presented to geologists than here.

Lower/Middle Ordovician boundary in the Babino Quarry.

Lower/Middle Ordovician boundary in the Babino Quarry.

The trace fossils along this boundary are complex and may show both boring and burrowing behavior.  The distinction depends on when the sediments were soft, firm and cemented, and on the varieties of organisms which did the work.

Borings in the Lower/Middle Ordovician boundary at Babino Quarry.

Borings in the Lower/Middle Ordovician boundary at Babino Quarry.

I can’t take these specimens home for further examination.  I’d very much like to make thin-sections (slices of rock shaved down until almost transparent for microscopic analysis) of all the critical intersections, but that will have to wait.  Andrey collected many samples he can cut up and share from his lab in Moscow.

Ordovician Hardgrounds

June 7th, 2009

SASS RIVER, LENINGRAD REGION, RUSSIA–The main geological attractions for me on this expedition are the abundant carbonate hardgrounds in the Lower and Middle Ordovician in this part of the world.  A carbonate hardground is a cemented seafloor.  What were soft sediments on the bottom were cemented with carbonate minerals (calcite in the Ordovician) so that they became a rocky surface several centimeters thick.  The sediment is usually carbonate mud and shells, so the result is essentially a limestone seafloor.  Many invertebrate animals colonize these hard surfaces by wither encrusting them or boring into them.  Those eocrinoids illustrated earlier, for example, often encrusted Early and Middle Ordovician hardgrounds.

Today at the Sass River Carbonate Mound locality (N60.02316°, E32.62471°) we saw numerous hardgrounds bored by a shallow variety of a trace fossil called Trypanites.

Borings in Ordovician hardground fragments.

Borings in Ordovician hardground fragments.

These are the most common borings in hardgrounds.  This particular type of Trypanites is remarkably shallow — often appearing as pits rather than the usual penetrating cylinder.  Another difference between these hardground fossil faunas and those I know best in North America and western Europe.